Welcome to the Prismic community, and thanks for sharing your question
As you suspect, this issue likely requires your developer. There are two possibilities:
- When your developer set up your Prismic repository, they set a field for preview title and preview image, but they're not obvious.
- Your developer has not set those fields, so the fields need to be configured in Prismic and programmed in your website.
If it's the first one, we might be able to figure this out without your developer. Often developers organize Prismic documents using tabs, like in this guide. Check to see if there are any tabs in your document. You can also let me know the name of the repo and the document type you're working with, and I can take a look. (You can send that in a DM if you don't want to share it publicly.)
If that doesn't work, the answer lies with your developer. Either way, your developer is the only one who definitely has the answer.
Let me know if you have any other questions.